1. Field of the Invention
The present invention relates to a leaf spring mechanism and a method of manufacturing the same and, more particularly, to an objective lens drive device into which the leaf spring system is incorporated.
2. Description of the Related Art
In the case of the leaf spring mechanism for linearly moving an object, two or more leaf springs are arranged substantially parallel to one another and fixedly held at one of their ends while the object to be moved is fixed to their other ends. When the leaf springs curve, the object is moved in a direction perpendicular to the planes of the leaf springs. This leaf spring mechanism is incorporated into the objective lens drive device of the optical system to move the objective lens in the focusing direction. The leaf spring mechanism enables the objective lens to move along its optical axis perpendicular to the surface of the optical disk, that is, in the focusing direction while keeping the optical axis substantially aligned with target information stored on the optical disk. A leaf spring mechanism of this kind is disclosed together with an optical disk system in Japanese Patent Disclosure Sho 61-123030. In the case of this leaf spring mechanism, two leaf springs 101 and 102 shaped like an isosceles triangle are arranged parallel to each other and an objective lens 103 is fixed to an apex of the triangle, as shown in FIG. 1. In the optical disk system into which the leaf spring mechanism is incorporated, the objective lens can be moved at high speed by a small force to gain quick access to the optical disk when the inertia moment of a rotating member 106 is made small while enhancing the vibrating characteristic of the objective lens 103 in focusing and tracking directions 104 and 105.
In order to form the leaf spring mechanism 100 keeping the upper and lower leaf springs 101 and 102 parallel to each other, the leaf springs 101 and 102 which are shaped like an isosceles triangle must be accurately positioned together with an objective lens holder 107 and the rotating member 106 and then molded as a unit to fix the holder 107 to the apex of the isosceles triangle and the rotating member 106 to the bottom side thereof. The leaf spring mechanism will become suitable for mass production when the above-mentioned components can be accurately positioned and then fixed according to the injection molding process. Durable beryllium copper, phosphor bronze, stainless steel or the like is used for the leaf springs 101 and 102 and thermosetting resin such as plastics is used for the injection molding process in this case.
However, these materials are different in coefficient of thermal expansion and strain is caused during cooling after the injection molding process so as to thereby break the parallel orientation of the leaf springs. The leaf spring mechanism thus made has a moving characteristic in a direction (or curved direction) perpendicular to the planes of the leaf springs to which is nonlinear. In the case where the leaf spring mechanism is incorporated into the optical disk device, resonance frequency in the plane direction of the leaf springs or tracking direction is greatly lowered and a servo-band needed to control the optical disk system cannot be sufficiently wide.
In the case where the leaf spring mechanism is molded according to the injection molding as described above, the parallel orientation of the leaf springs is lost because the material by which the leaf springs are made is different in coefficient of thermal expansion from the other material which is used for the injection molding. Therefore, the leaf spring mechanism thus made has a nonlinear moving characteristic in the curving direction. Further, when the leaf spring mechanism is incorporated into the optical disk system, the resonance frequency in the direction perpendicular to the curving direction, that is, in the tracking direction, is extremely lowered and a servo-band needed to control the optical disk device cannot be sufficiently wide.